1. Field of the Invention
This invention relates to integrally molded articles of thermoplastic resin and oil-bleeding silicone rubber which can be easily and briefly molded by means of injection molding machines and which will find use in electric, electronic, automotive and precision machinery applications.
2. Prior Art
A number of techniques are known in the art for bonding addition curing type silicone rubber to organic resins. For example, a molded resin on the surface is coated with a primer and a curable silicone rubber is applied and cured thereto. Another joining technique is to cure a self-adhesive silicone rubber composition to a molded resin. There are known a number of patents relating to self-adhesive silicone rubber compositions, especially adhesive components thereof. Japanese Patent Publication (JP-B) No. 34311/1990 corresponding to EP 143994A discloses that an organopolysiloxane containing more than 30 mol % of a hydrogen atom directly attached to a silicon atom is added to an organic resin which is joined to an addition curing type silicone rubber. In JP-B 45292/1988, silicone rubber is physically fitted in an organic resin. Japanese Patent Application Kokai (JP-A) No. 183843/1988 corresponding to 276790 discloses a method of integrally joining silicone rubber to an olefin resin having grafted thereto a compound containing an aliphatic unsaturated group and a hydrolyze group attached to a silicon atom. In JP-A 111981/1993 corresponding to U.S. Pat. No. 5,366,806 by the same assignee as the present invention, silicone rubber is integrally joined to a thermoplastic resin having added thereto a compound containing an unsaturated group and a hydrogen atom directly attached to a silicon atom.
These methods, however, have more or less problems. The method using a primer is cumbersome in that a once molded resin part must be taken out of the mold before a primer can be applied. The method of curing a self-adhesive silicone rubber material to a molded resin has the serious problem that when the silicone rubber-coated resin is molded in a mold, the silicone rubber itself adheres to the mold. Insofar as silicone rubber is applied and cured to resin moldings, no problems occur on practical use. However, addition curable silicone self-adhesive compositions do not provide sufficient bonding forces when integrally molded with several of versatile resins, for example, ABS, PPO, PPS, polycarbonate, acryl, PE, PP and Teflon resins. Among the above-mentioned proposals, the method of adding hydrogenpolysiloxane to olefin resins has the problem that the resin is less likely to exert its inherent properties because the properties of the resin itself can be altered by the siloxane added thereto. The physical engagement between silicone rubber and organic resin can be disrupted by physical forces. The use of an olefin resin having grafted thereto a compound containing an aliphatic unsaturated group and a hydrolyzable group attached to a silicon atom requires a primer for the integration of an addition curing type silicone rubber.
As silicone rubber is recognized highly reliable with respect to heat resistance, weather resistance and electrical properties, it finds expanding application to electric, electronic and automotive fields. Since oil seals, connectors, O-rings, and other automotive parts require operation efficiency upon assembly, tightness and insulation as mounted, it is desirable and advantageous to provide integrally molded articles having a thermoplastic resin firmly joined to an oil-bleeding silicone rubber allowing oil to bleed to the surface after molding.
In this regard, we already proposed in JP-A 171021/1994 and 171023/1994 corresponding to U.S. Pat. No. 5,366,805 and U.S. Pat. No. 5,418,065 an integrally molded article wherein a thermoplastic resin containing an aliphatic unsaturated group and a silicone rubber containing a specific adhesive agent are integrally molded to form a firm joint therebetween. No reference was made to joint with oil-bleeding silicone rubber because such bonding was technically difficult at that time.